1. Field of the Invention
The invention relates to ophthalmic and other types of surgical and non-surgical use blades and mechanical devices. More particularly, the invention relates to ophthalmic, micro-surgical and non-surgical blades and mechanical devices manufactured from single crystal silicon and other single or poly-crystalline materials, and processes for manufacture and strengthening of the aforementioned mechanical devices, surgical and non-surgical blades.
2. Description of the Related Art
Existing surgical blades are manufactured via several different methodologies, each method having its own peculiar advantages and disadvantages. The most common method of manufacture is to mechanically grind stainless steel. The blade is subsequently honed (through a variety of different methods such as ultrasonic slurrying, mechanical abrasion and lapping) or is electrochemically polished to achieve a sharp edge. The advantage of these methods is that they are proven, economical processes to make disposable blades in high volume. The greatest disadvantage of these processes is that the edge quality is variable, such that achieving superior sharpness consistency is still a challenge. This is primarily due to the inherent limitations of the process itself. Blade edge radii can range from 30 nm to 1000 nm.
A relatively new method of blade manufacture employs coining of the stainless steel in lieu of grinding. The blade is subsequently electrochemically polished to achieve a sharp edge. This process has been found to be more economical than the grinding method. It has also been found to produce blades with better sharpness consistency. The disadvantage of this method is that the sharpness consistency is still less than that achieved by the diamond blade manufacturing process. The use of metal blades in soft tissue surgery is prevalent today due to their disposable cost and their improved quality.
Diamond blades are the gold standard in sharpness in many surgical markets, especially in the ophthalmic surgery market. Diamond blades are known to be able to cleanly cut soft tissue with minimal tissue resistance. The use of diamond blades is also desired due to their consistent sharpness, cut after cut. Most high-volume surgeons will use diamond blades since the ultimate sharpness and sharpness variability of metal blades is inferior to that of diamond. The manufacturing process used to make diamond blades employs a lapping process to achieve an exquisitely sharp and consistent edge radius. The resultant blade edge radii range from 5 nm to 30 nm. The disadvantage of this process is that it is slow and as a direct result, the cost to manufacture such diamond blades ranges from $500 to $5000. Therefore, these blades are sold for reuse applications. This process is currently used on other, less hard materials, such as rubies and sapphires, to achieve the same sharpness at a lesser cost. However, while less expensive than diamonds, ruby and/or sapphire surgical quality blades still suffer from the disadvantage that the cost of manufacture is relatively high, ranging from $50 to $500, and their edges only last through about two hundred cases. Therefore, these blades are sold for reuse and limited reuse applications.
There have been a few proposals for the manufacture of surgical blades using silicon. However, in one form or another, these processes are limited in their ability to manufacture blades in various configurations and at a disposable cost. Many of the silicon blade patents are based on anisotropic etching of silicon. The anisotropic etching process is one where the etching is highly directional, with different etch rates in different directions. This process can produce a sharp cutting edge. However, due to the nature of the process, it is limited by the blade shapes and included bevel angles that can be attained. Wet bulk anisotropic etching processes, such as those employing potassium hydroxide (KOH), ethylene-diamine/pyrcatechol (EDP) and trimethyl-2-hydroxethylammonium hydroxide (TMAH) baths, etch along a particular crystalline plane to achieve a sharp edge. This plane, typically the (111) plane in silicon <100>, is angled 54.7° from the surface plane in the silicon wafers. This creates a blade with an included bevel angle of 54.7°, which has been found to be clinically unacceptable in most surgical applications as too obtuse. This application is even worse when this technique is applied to making double bevel blades, for the included bevel angle is 109.4°. The process is further limited to the blade profiles that it can produce. The etch planes are arranged 90° to each other in the wafer. Therefore, only blades with rectangular profiles can be produced.
In the methods described in greater detail below for manufacturing surgical and non-surgical blades and other mechanical devices from silicon, it is possible that mechanical damage can be induced into the brittle silicon material during one or more of the machining steps. Cracks, chips, scratches and sharp edges all act as crack initiation points in brittle materials. These points serve to initiate catastrophic failure of mechanical devices when they are loaded or stressed.
Other methods are well known to produce sharpened edges in blades formed from wafers in which a photomask is used along with an isotropic wet or dry etch to etch through the wafer to form an ophthalmic blade geometry and the cutting edge. In this process the entire perimeter of the blade etches through and forms a sharpened edge. This thru-etching occurs only while an etch mask is in place. The mask defines approximately where the cutting edges will be created. The mask is then removed and the blades float free when their carrier is dissolved (requiring an additional die level cleaning step). This is both inefficient and ineffective for volume production of high quality, defect free ophthalmic blades. It is inefficient because it adds steps to the manufacturing process.
There are also significant cutting edge geometry constraints inherent to this process. The bevel created by this process is limited to an inefficient 45° for a single bevel blade and an impractical 90° for a double bevel blade. Further, the width of the bevel is severely constrained by the process to a maximum of one times the thickness of the wafer for a single bevel blade and one-half the thickness of the wafer for a double bevel blade. These geometries result in a poor cutting tool as evidenced by a lack of adoption in the ophthalmic community.
Thus, a need exists to manufacture blades that address the shortcomings of the methods discussed above. This system and method of the present invention can make blades with the sharpness of diamond blades at the disposable cost of the stainless steel methods. In addition, the system and method of the present invention can produce blades in high volume and with tight process control. Further, the system and method of the present invention can produce surgical and various other types of blades with both linear and non-linear blade bevels. Still further, the system and method of the present invention can remove the mechanical damage induced into the silicon crystalline material when blades (surgical or non-surgical) or other mechanical devices are manufactured according to the processes described herein.